1. Technical Field
The present invention relates to a piezoelectric film producing process, a vibrator element that includes a piezoelectric film produced by the process, and vibrators, oscillators, electronic devices, and moving objects that include the vibrator element.
2. Related Art
A piezoelectric thin film resonator (hereinafter, referred to as “vibrator element”) is known that is configured to include a lower electrode provided on a substrate, a piezoelectric film provided on the lower electrode, and an upper electrode provided on the piezoelectric film, and having a region opposite the lower electrode with the piezoelectric film in between (see, for example, JP-A-2013-34130).
The vibrator element uses aluminum nitride (hereinafter, “AlN”) for the piezoelectric film. The piezoelectric film is deposited (formed) by sputtering, using Al (aluminum) as the target material (deposition material) in a mixed atmosphere of N2 (nitrogen) gas and Ar (argon) gas.
However, because the piezoelectric film uses pure aluminum as deposition material, processes such as the deposition of the upper electrode after the AIN deposition may produce internal stress in the aluminum present at the crystal grain boundaries of the deposited AlN.
The piezoelectric film thus involves the risk of generating stress migration, forming voids in the aluminum.
The resulting degradation of electromechanical coupling coefficient increases the impedance of the piezoelectric film. This may cause deterioration in the function of the piezoelectric film, and the reliability (long-term reliability in particular) may suffer as a result of the progression of stress migration (e.g., void diffusion).
This may lead to an increase in the CI (crystal impedance) value of the vibrator element that includes the piezoelectric film, and the vibration characteristics and the reliability of the vibrator element may suffer.